1. Field of the Invention
The invention is directed to the removal or prevention of ice buildup on aircraft surfaces, and more particularly to the incorporation of a perforated heating element which forms one lamination layer within the laminated layers of perforated sound attenuation or suppression structures associated with a gas turbine engine.
2. Brief Description of the Prior Art
The application of gas turbine engines to aircraft has introduced a serious icing problem in view of the particular vulnerability of gas turbine engines to ice formation. The formation of ice on such air intake components as the intake fairing, the nose bullet, and the struts supporting the front bearing of the engine, causes serious obstruction to the flow of air passing into the engine compressor and may cause considerable damage resulting from pieces of ice breaking loose from such components and being carried by the air stream into damaging contact with the rotating parts of the engine. Prior art methods for alleviating this problem include the introduction of alcohol, hot gases, and by the application of heat to the ice buildup areas.
A de-icing liquid such as, alcohol can only be used where actual ice buildup is detected and, because of the weight of such liquid, only small quantities can be carried in the aircraft and, therefore, can only be sparingly used.
Heated air bled from the gas turbine engine is very very effective and can be continuously applied. However, heated air cannot be used in all areas required because modern aircraft employ Helmholtz resonant acoustic material and other similar types of material for sound suppression in ice buildup areas. Helmholtz and similar acoustic material generally employ a multiplicity of perforations in their outer surface thereby making the use of heated air to preclude ice formation impracticable.
Examples of the prior art acoustic laminate material to which the present invention is generally directed, can be found in U.S. Pat. Nos. 4,254,171; 4,318,453; 4,379,191; 4,384,020; and 4,421,811, all of which are assigned to the assignee of the instant invention.
Until the emergence of this invention there has not been an effective way to eliminate ice buildup on acoustically treated aircraft surfaces.